The present disclosure relates to data storage devices. In particular, the present disclosure relates to techniques for setting load distributions on storage media using multiple writers.
Data storage devices, such as disc drives, typically store information on surfaces of storage media, such as magnetic or optical discs. In a typical disc drive, one or more discs are mounted together on a spindle motor. The spindle causes the disc(s) to spin and the data surfaces of the disc(s) to pass under respective bearing sliders. A transducing head carried by a slider is used to read from and write to a data track on a disc. The slider is typically carried by a head arm assembly that includes an actuator arm and a suspension assembly, which can include a separate gimbal structure or can integrally form a gimbal. During operation, as the disc spins, the slider glides above the surface of the disc on a small cushion of air, and the actuator arm pivots to movably position the slider with respect to the disc.
The transducing head typically includes a writer and a reader. The reader includes a sensor for retrieving magnetically encoded information stored on the disc (or other magnetic storage media). Magnetic flux from the surface of the disc causes rotation of the magnetization vector of a sensing layer or layers of the sensor, which in turn causes a change in the electrical properties of the sensor that can be detected by passing a current through the sensor and measuring a voltage across the sensor. Depending on the geometry of the sensor, the sensed current may be passed in the plane (CIP) of the layers of the sensor or perpendicular to the plane (CPP) of the layers of the sensor. External circuitry then converts the voltage information into an appropriate format and manipulates that information as necessary to recover information encoded on the disc.
The writer, for a perpendicular recording transducing head, typically includes a main pole and a return pole, which are separated from each other at an air bearing surface (ABS) of the transducing head by a gap layer. The main pole and return pole are connected to each other at a region distal from the ABS by a back gap closer or back via. One or more layers of conductive coils are typically positioned between the main and return poles, and are encapsulated by insulating layers. The conductive coils can have different configurations, such as helical and pancake configurations. To write data to the disc (or other magnetic media), an electric current is applied to the conductive coils to induce a magnetic field in the disc under a pole tip of the main pole. By reversing the direction of the current through the coils, the polarity of the data written to the magnetic media is reversed, and a magnetic transition is written between two adjacent bits. Because the main pole is generally the trailing pole of the main and return poles, the main pole is typically used to write the data to the magnetic media.
As areal recording densities for storage discs increase, the sizes of sliders and transducing heads continue to decrease. Moreover, the track widths of individual concentric data tracks on the storage discs continue to decrease. Decreasing slider sizes and disc track widths present numerous difficulties. For example, with perpendicular recording heads, magnetization transitions are recorded on the magnetic medium (e.g., disc) by a trailing edge of the main pole. The shape of the pole tip of the main pole is projected and reproduced on the magnetic medium during the write process. However, unwanted overwriting or side writing at locations adjacent to a desired write location on a data track may occur due to changes in the skew angle as the transducing head travels in an arc across the magnetic medium as the actuator arm and suspension pivot. Skew angles are typically most prominent at the inner and outer diameter regions of the disc. This can cause adjacent track interference, resulting in off track erasure of transitions recorded on the magnetic medium, and ultimately leading to a degradation of bit error rate. Accordingly, there is an ongoing need to attain high areal densities on recording media to meet the increased demand for high capacity data storage devices.